I would try to exit steam, then try to launch steam as an administrator and see if that helps.

(the xbox live error appears to be a red herring, that’s just the last error reported but its likely the next process is dying but not writing to a log)

Do you have a crash report that you could upload here, please?:

1. After the crash has occurred, a pop-up window prompting you to enter the details of what you were doing prior to the crash will be displayed
2. Submit the pop-up window
3. Another pop-up window similar to the previous one will be displayed
4. Click the ‘Copy to clipboard’ button